Impact rock crushing is a method of producing specific aggregates that are able to meet with the higher engineering standards governing newer, more specialized construction projects. It is commonly known in the construction industry that aggregates having four or more clean, fractured surfaces with relatively cubical shape enhance the strength-durability of concrete and asphalt. Aggregates having these qualities mix more thoroughly and provide a finished product having greater compression/elongation strength. An increased number of clean, fractured surfaces on the aggregate enable concrete or asphalt to adhere more completely to the aggregate, enabling improved compaction and stability.
It is known to produce aggregates using eccentric-type rock crushers (also known as cone crushers). This type of rock crusher has been in use for many decades. These machines are very efficient and make up the majority of tertiary rock crushers in use. Cone crushers produce aggregate materials at relatively low cost since they utilize substantially concave and cone shaped mantle castings which provide outstanding wear resistance. These components, made of work hardening manganese steel, typically last several hundred thousand tonnes of crushed product; which could represent many weeks of production before requiring replacement. Cone crushers also have a high rate of production, however, the physical rock shapes they produce tend to be elongated, which reduces the possibility of consistently achieving optimum compression/elongation strength required in specialized batches of concrete or asphalt. Cone crushers wedge the larger feed rock into a controlled-restricted cavity and the wedging forces created fractures the feed rock into smaller sizes. This type of controlled crushing forces the feed rock to crush more elongated, thus producing a greater percentage of finished product that is less than cubical, or for those familiar with this industry, “arrow heads”.
It is also known to use impact crushers, more specifically, vertical shaft impactor (“VSI”) rock crushers as depicted as “A” in FIG. 1. They are unique in that they produce a crushed aggregate that is not fractured in a confined cavity, but openly fractured by direct impact. VSI rock crushers create a finished product that has multiple clean fractured surfaces and tends to be more cubical since the rock can fracture naturally.
Referring back to FIG. 1, feed rock “C” to be crushed into aggregate “I” is introduced into VSI rock crusher “A” via hopper “B”. Feed rock “C” lands on rotating table “D”. Table “D” is rotated by shaft “J” having pulley “K”. Pulley “K” is driven by a belt and a motor (not shown). Impellers “E” on table “D” throw feed rock “C” towards the outer walls of VSI rock crusher “A” where feed rock “C” strikes anvils “F”. Anvils “F” are supported by hanger “G” that are, in turn, secured to bracket ring “H”. Table “D” turns at a sufficient speed such that feed rock “C” impacts anvils “F” with sufficient force to cause feed rock “C” to break into smaller pieces that form aggregate “I”. The rotational speed of table “D” can exceed 300 RPM, which will generate sufficient impact velocity to feed rock “C”. FIG. 2 shows a perspective view of VSI rock crusher “A”, table “D”, impellers “E”, anvils “F”, hanger brackets “G” and bracket ring “H”.
As effective as VSI rock crushers are in producing “higher spec” aggregates, the wear components utilized, i.e. impellers “E” and anvils “F”, are physically smaller as compared to cone crushers. Accordingly, they wear out relatively quickly. Anvils and impellers are, typically, alloy castings that are expensive and may only last one or two production shifts. The higher wear rate of impellers and anvils results in more frequent maintenance of VSI rock crushers, namely, replacing worn out impellers and anvils. Accordingly, impactor crushing can be more expensive than cone crushing. In addition, impellors and anvils are cast items that can weigh over 100 pounds each. The manhandling of these items as they are replaced in VSI rock crushers can be hazardous.
Referring to FIGS. 3 and 4, a typical prior art anvil “F” is shown having integral lug “M” with lug flanges “N”. As illustrated, lug “M” is positioned vertically with respect to anvil “F”. Flanges “N” are used to secure anvil “F” to hanger bracket “G” as shown in FIGS. 5 and 6. Hanger bracket “G” has slot “L” that is sized to receive lug “M” and to prevent anvil “F” from rotating when seated in hanger bracket “G”. Flanges “N” rest on the backside of hanger bracket “G” to keep anvil “F” upright. As shown, lug “M” has a rectangular cross-section. This configuration allows anvil “F” to be placed into bracket “G” in one of two possible positions. Referring to FIG. 7, a typical wear pattern on anvil “F” is illustrated. As feed rock “C” is thrown towards anvils “F” by impellers “E” on table “D”, feed rock “C” will cause wear pattern “O” on the impact face of anvils “F”. Once wear pattern “O” has approached or reached the maximum permissible wear, anvil “F” can be lifted from bracket “G” rotated 180° and placed back into bracket “G” to present a second wear surface. After the maximum permissible wear has been reached on this second surface, anvil “F” is then replaced with a new anvil.
It is, therefore, desirable to provide an improved vertical shaft impactor rock crusher where the improvement provides anvils that have extended wear characteristics over prior art anvils.